Plasma processing method and plasma processing apparatus

ABSTRACT

A plasma processing method performs an etching process of supplying a fluorine-containing gas into a plasma processing space and etching a target substrate, in which a silicon oxide film or a silicon nitride film is formed on a surface of a nickel silicide film, with plasma of the fluorine-containing gas (process S 101 ). Then, the plasma processing method performs a reduction process of supplying a hydrogen-containing gas into the plasma processing space and reducing, with plasma of the hydrogen-containing gas, a nickel-containing material deposited on a member, of which a surface is arranged to face the plasma processing space, after the etching process (process S 102 ). Thereafter, the plasma processing method performs a removal process of supplying an oxygen-containing gas into the plasma processing space and removing nickel, which is obtained by reducing the nickel-containing material in the reduction process, with plasma of the oxygen-containing gas (process S 103 ).

CROSS-REFERENCE TO RELATED APPLICATION

This application is a U.S. national phase application under 35 U.S.C.§371 of PCT Application No. PCT/JP2013/072893 filed on Aug. 27, 2013,which claims the benefit of Japanese Patent Application No. 2012-189063filed on Aug. 29, 2012, and U.S. Provisional Application Ser. No.61/696,435 filed on Sep. 4, 2012, the entire disclosures of which areincorporated herein by reference.

TECHNICAL FIELD

The embodiments described herein pertain generally to a plasmaprocessing method and a plasma processing apparatus.

BACKGROUND

In a semiconductor manufacturing process, a plasma processing apparatusthat performs a plasma process of etching or depositing a thin film hasbeen widely used. Examples of the plasma processing apparatus mayinclude a plasma CVD (Chemical Vapor Deposition) apparatus that performsa deposition process of a thin film or a plasma etching apparatus thatperforms an etching process.

The plasma processing apparatus includes, for example, a processingvessel that partitions a plasma processing space; a sample table thatmounts a target substrate thereon within the processing vessel; and agas supply system that supplies a processing gas for plasma reactioninto the processing vessel. Further, the plasma processing apparatusalso includes a plasma generation device that supplies electromagneticenergy such as a microwave, a RF wave, etc. to excite the processing gaswithin the processing vessel into plasma; and a bias voltage applicationdevice that applies a bias voltage to the sample table to accelerateions in the plasma toward the target substrate mounted on the sampletable.

Meanwhile, it has been known that in a plasma processing apparatus, whenforming contact holes for field effect transistor (FET), a targetsubstrate, in which a silicon oxide film or a silicon nitride film isformed on a surface of a silicide film, is etched. In this regard, forexample, Patent Document 1 describes that a target substrate, in which asilicon oxide film or a silicon nitride film is formed on a surface of anickel silicide film, is arranged in a plasma processing space, and thetarget substrate is etched toward the nickel silicide film serving as abase.

Patent Document 1: Japanese Patent Laid-open Publication No. 2010-080798

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

However, in the conventional technology, there has been a risk thatetching characteristics of the target substrate are degraded (changed)with a lapse of time. That is, in the convention technology, when thetarget substrate is etched toward the nickel silicide film serving as abase film, the nickel silicide film itself may be etched. For thisreason, in the conventional technology, a nickel-containing materialgenerated from the etched nickel silicide film is accumulativelydeposited on various components facing the plasma processing space, sothat plasma density within the plasma processing space is varied. As aresult, the etching characteristics of the target substrate may bedegraded (changed) with a lapse of time.

Means for Solving the Problems

In one example embodiment, a plasma processing method is performed in aplasma processing apparatus, and the plasma processing method includes afirst process, a second process and a third process. In the firstprocess, a fluorine-containing gas is supplied into a plasma processingspace and a target substrate, in which a silicon oxide film or a siliconnitride film is formed on a surface of a nickel silicide film, is etchedwith plasma of the fluorine-containing gas. Further, in the secondprocess, a hydrogen-containing gas is supplied into the plasmaprocessing space and a nickel-containing material deposited on a member,of which a surface is arranged to face the plasma processing space, isreduced with plasma of the hydrogen-containing gas, after the firstprocess. Furthermore, in the third process, an oxygen-containing gas issupplied into the plasma processing space and nickel, which is obtainedby reducing the nickel-containing material in the second process, isremoved with plasma of the oxygen-containing gas.

Effect of the Invention

In accordance with various example embodiments, it is possible toprovide a plasma processing method and a plasma processing apparatus,capable of suppressing etching characteristics of the target substratefrom being degraded (changed) with a lapse of time.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal cross-sectional view illustrating a schematicconfiguration of a plasma processing apparatus in accordance with anexample embodiment.

FIG. 2 is a diagram illustrating a configuration example of a wafer tobe etched in the plasma processing apparatus in accordance with theexample embodiment.

FIG. 3 is an explanatory diagram illustrating a mechanism of degradation(change) of etching characteristics of the wafer with a lapse of timewhen a nickel-containing material is deposited on an electrode plate ofan upper electrode.

FIG. 4A is a diagram illustrating a model example in which thenickel-containing material is deposited on the electrode plate of theupper electrode.

FIG. 4B is a diagram illustrating a model example in which thenickel-containing material is deposited on the electrode plate of theupper electrode.

FIG. 5A is a diagram illustrating a model example of a plasma process inaccordance with the present example embodiment.

FIG. 5B is a diagram illustrating a model example of the plasma processin accordance with the present example embodiment.

FIG. 5C is a diagram illustrating a model example of the plasma processin accordance with the present example embodiment.

FIG. 6 is a flow chart of the plasma process in accordance with anexperimental example.

FIG. 7 is a diagram (first diagram) for explaining an effect of a plasmaprocessing method in accordance with the present example embodiment.

FIG. 8 is a diagram (second diagram) for explaining an effect of theplasma processing method in accordance with the present exampleembodiment.

MODE FOR CARRYING OUT THE INVENTION

Hereinafter, various example embodiments will be explained in detailwith reference to the accompanying drawings. Further, in the drawings,the same or corresponding components will be respectively assigned thesame reference numerals.

In one example embodiment, a plasma processing method performed in aplasma processing apparatus includes a first process of supplying afluorine-containing gas into a plasma processing space to generateplasma of the fluorine-containing gas and etching a target substrate, inwhich at least one of a silicon oxide film and a silicon nitride film isformed on a surface of a nickel silicide film, with the plasma of thefluorine-containing gas; a second process of supplying ahydrogen-containing gas into the plasma processing space to generateplasma of the hydrogen-containing gas and reducing, with the plasma ofthe hydrogen-containing gas, a nickel-containing material deposited on amember, of which a surface is arranged to face the plasma processingspace, after the first process; and a third process of supplying anoxygen-containing gas into the plasma processing space to generateplasma of the oxygen-containing gas and removing nickel, which isobtained by reducing the nickel-containing material in the secondprocess, with the plasma of the oxygen-containing gas. Further,variation in Vpp on the target substrate is suppressed by removing thenickel-containing material deposited on the member, of which the surfaceis arranged to face the plasma processing space, through the secondprocess and the third process.

The second process and the third process may be repeatedly performed atleast twice.

The second process may be performed by supplying the hydrogen-containinggas and a nitrogen-containing gas.

The nitrogen-containing gas may be at least one of a N₂ gas, a NH₃ gas,and a N₂H₂ gas.

The hydrogen-containing gas may be at least one of a H₂ gas, a CH₃F gas,a CH₂F₂ gas, a CHF₃, a NH₃ qas, a N₂H₂ gas.

The oxygen-containing gas may be at least one of O₂ gas, a CO₂ gas, anda CO gas.

In another example embodiment, a plasma processing apparatus includes aprocessing vessel configured to partition a plasma processing spaceaccommodating therein a target substrate, in which at least one of asilicon oxide film and a silicon nitride film is formed on a surface ofa nickel silicide film; a first gas supply unit configured to supply afluorine-containing gas into the plasma processing space; a second gassupply unit configured to supply a hydrogen-containing gas into theplasma processing space; a third gas supply unit configured to supply anoxygen-containing gas into the plasma processing space; and a controlunit configured to perform a first process of supplying thefluorine-containing gas into the plasma processing space from the firstgas supply unit to generate plasma of the fluorine-containing gas andetching the target substrate with the plasma of the fluorine-containinggas; a second process of supplying the hydrogen-containing gas into theplasma processing space from the second gas supply unit to generateplasma of the hydrogen-containing gas and reducing, with the plasma ofthe hydrogen-containing gas, a nickel-containing material deposited on amember, of which a surface is arranged to face the plasma processingspace, after the first process; and a third process of supplying theoxygen-containing gas into the plasma processing space from the thirdgas supply unit to generate plasma of the oxygen-containing gas andremoving nickel, which is obtained by reducing the nickel-containingmaterial in the second process, with the plasma of the oxygen-containinggas and configured to suppress variation in Vpp on the target substrateby removing the nickel-containing material deposited on the member, ofwhich the surface is arranged to face the plasma processing space,through the second process and the third process. Further, the variationin the Vpp on the target substrate is suppressed by removing thenickel-containing material deposited on the member, of which the surfaceis arranged to face the plasma processing space, through the secondprocess and the third process.

FIG. 1 is a longitudinal cross-sectional view illustrating a schematicconfiguration of a plasma processing apparatus in accordance with anexample embodiment. As depicted in FIG. 1, a plasma processing apparatus1 includes a substantially cylindrical processing vessel 11 havingtherein a plasma processing space S in which a plasma process isperformed. The processing vessel 11 is electrically grounded via aground line 12. Further, a surface of the processing vessel 11 faces theplasma processing space S. That is, the processing vessel 11 is providedsuch that the surface thereof faces the plasma processing space S.

Within the processing vessel 11, a wafer chuck 10 configured to hold awafer W as a target substrate is provided. A bottom surface of the waferchuck 10 is supported on a susceptor 13 serving as a lower electrode.The susceptor 13 is made of a metal such as aluminum and has asubstantially disk shape. A supporting table 15 is provided at a bottomof the processing vessel 11 via an insulating plate 14, and thesusceptor 13 is supported on a top surface of the supporting table 15.An electrode (not illustrated) is embedded in the wafer chuck 10, andthe wafer chuck 10 is configured to attract and hold the wafer W by anelectrostatic force generated by applying a DC voltage to the electrode.

A conductive focus ring 20 made of, for example, silicon is provided onan outer peripheral portion of the wafer chuck 10 as a top surface ofthe susceptor 13 in order to improve uniformity of a plasma process.Outer side surfaces of the susceptor 13, the supporting table 15, andthe focus ring 20 are covered with a cylindrical member 21 made of, forexample, quartz. Further, a surface of the focus ring 20 faces theplasma processing space S. That is, the focus ring 20 is provided suchthat the surface thereof faces the plasma processing space S.

Within the supporting table 15, a coolant path 15 a configured to allowa coolant to flow therein is formed into, for example, a circular ringshape. By adjusting a temperature of the coolant supplied into thecoolant path 15 a, a temperature of the wafer W held on the wafer chuck10 can be controlled. Further, a heat transfer gas line 22 configured tosupply a heat transfer gas, e.g., a helium gas into a gap between thewafer chuck 10 and the wafer W held on the wafer chuck 10 is provided topass through, for example, the susceptor 13, the supporting table 15,and the insulating plate 14.

The susceptor 13 is electrically connected to a first high frequencypower supply 30 configured to apply a high frequency power for plasmageneration to the susceptor 13 via a first matching device 31. The firsthigh supply power supply 30 is configured to output a high frequencypower having a frequency of, for example, from 27 MHz to 100 MHz, e.g.,40 MHz in the present example embodiment. The first matching device 31is configured to match internal impedance of the first high frequencypower supply 30 with load impedance, and to allow the internal impedanceof the first high frequency power supply 30 and the load impedance to beapparently matched with each other when plasma is generated within theprocessing vessel 11.

Further, the susceptor 13 is also electrically connected to a secondhigh frequency power supply 40 configured to apply a bias voltage forion attraction into the wafer W by applying a high frequency power tothe susceptor 13 via a second matching device 41. The second highfrequency power supply 40 is configured to output a high frequency powerhaving a frequency of, for example, from 400 kHz to 13.56 MHz, e.g.,13.56 MHz in the present example embodiment. The frequency of the highfrequency power outputted from the second high frequency power supply 40is lower than the frequency of the high frequency power outputted fromthe first high frequency power supply 30. Like the first matching device31, the second matching device 41 is also configured to match internalimpedance of the second high frequency power supply 40 with loadimpedance.

The first high frequency power supply 30, the first matching device 31,the second high frequency power supply 40, and the second matchingdevice 41 are connected to a control unit 150 to be described later, andthe overall operations thereof are controlled by the control unit 150.

Above the susceptor 13 as the lower electrode, an upper electrode 42 isprovided to face the susceptor 13 in parallel. The upper electrode 42 issupported on a ceiling portion of the processing vessel 11 via aconductive supporting member 50. Accordingly, the upper electrode 42 isalso electrically grounded like the processing vessel 11.

The upper electrode 42 includes an electrode plate 51 that forms asurface of the upper electrode 42 facing the wafer W held on the waferchuck 10; and an electrode supporting body 52 that supports theelectrode plate 51 from above. Multiple gas discharge holes 53configured to supply a processing gas into the processing vessel 11 areformed through the electrode plate 51. The electrode plate 51 is madeof, for example, a semiconductor or a conductor having low Joule heatand low resistance, and in the present example embodiment, for example,silicon is used. Further, a surface of the electrode plate 51 facing thewafer W faces the plasma processing space S. That is, the electrodeplate 51 is provided such that the surface thereof faces the plasmaprocessing space S.

The electrode supporting body 52 is made of a conductor, and in thepresent example embodiment, for example, aluminum is used. A gasdiffusion space 54 having a substantially disk shape is formed in acentral portion within the electrode supporting body 52. Multiple gasthrough holes 55 extended downwards from the gas diffusion space 54 areformed in a lower portion of the electrode supporting body 52, and thegas discharge holes 53 communicate with the gas diffusion space 54 viathe gas through holes 55.

The gas diffusion space 54 is connected to a gas supply line 71. The gassupply line 71 is connected to a processing gas supply source 72 asillustrated in FIG. 1, and the processing gas supplied from theprocessing gas supply source 72 is introduced into the gas diffusionspace 54 via the gas supply line 71. The processing gas introduced intothe gas diffusion space 54 is then discharged into the processing vessel11 through the gas through holes 55 and the gas discharge holes 53. Thatis, the upper electrode 42 serves as a shower head configured to supplythe processing gas into the processing vessel 11.

In the present example embodiment, the processing gas supply source 72includes a gas supply unit 72 a, a gas supply unit 72 b, a gas supplyunit 72 c, and a gas supply unit 72 d. The gas supply unit 72 a isconfigured to supply a fluorine-containing gas as an etching gas intothe plasma processing space S. The fluorine-containing gas is, forexample, a C₄F₆ gas and a CH₂F₂ gas. Further, an O₂ gas is appropriatelyadded to the fluorine-containing gas. The gas supply unit 72 a is anexample of the first gas supply unit configured to supply thefluorine-containing gas into the plasma processing space S.

The gas supply unit 72 b is configured to supply a hydrogen-containinggas as a reducing gas after an etching process into the plasmaprocessing space S. The hydrogen-containing gas is at least any one of,for example, a H₂ gas, a CH₃F gas, a CH₂F₂ gas, and a CHF₃ gas. The gassupply unit 72 b is an example of the second gas supply unit configuredto supply the hydrogen-containing gas into the plasma processing spaceS.

The gas supply unit 72 c is configured to supply an oxygen-containinggas as a removing gas of deposit after a reduction process into theplasma processing space S. The oxygen-containing gas is at least any oneof, for example, an O₂ gas, a CO₂ gas, and a CO gas. The gas supply unit72 c is an example of the third gas supply unit configured to supply theoxygen-containing gas into the plasma processing space S.

Further, the gas supply unit 72 d is configured to supply anitrogen-containing gas as a reducing gas after the etching process intothe plasma processing space S. The nitrogen-containing gas is, forexample, a N₂ gas. Although not illustrated, the processing gas supplysource 72 supplies gases (for example, an Ar gas, and the like) to beused for various processes in the plasma processing apparatus 1.

Furthermore, the processing gas supply source 72 includes valves 73 a,73 b, 73 c, and 73 d and flow rate controllers 74 a, 74 b, 74 c, and 74d respectively provided between the gas supply units 72 a, 72 b, 72 c,and 72 d and the gas diffusion space 54. The flow rates of the gasessupplied into the gas diffusion space 54 are controlled by the flow ratecontrollers 74 a, 74 b, 74 c, and 74 d.

A gas exhaust path 80 serving as a flow path through which an atmospherewithin the processing vessel 11 is exhausted to the outside of theprocessing vessel 11 is formed between an inner wall of the processingvessel 11 and an outer side surface of the cylindrical member 21 at abottom portion of the processing vessel 11. A gas exhaust opening 90 isformed at a bottom surface of the processing vessel 11. A gas exhaustchamber 91 is provided under the gas exhaust opening 90, and a gasexhaust device 93 is connected to the gas exhaust chamber 91 via a gasexhaust line 92. By operating the gas exhaust device 93, the atmospherewithin the processing vessel 11 is exhausted through the gas exhaustpath 80 and the gas exhaust opening 90, and, thus, the inside of theprocessing vessel 11 can be depressurized to a preset vacuum level.

Around the processing vessel 11, a ring magnet 100 is arranged to beconcentric with the processing vessel 11. By the ring magnet 100, amagnetic field can be formed in a space between the wafer chuck 10 andthe upper electrode 42. The ring magnet 100 is configured to berotatable by a non-illustrated rotation unit.

Further, a control unit 150 is provided in the plasma processingapparatus 1. The control unit 150 is, for example, a computer includinga program storage unit (not illustrated) as a storage device, forexample, a memory. The program storage unit also stores a program ofoperating the plasma processing apparatus 1 by controlling therespective power supplies 30 and 40 or the respective matching devices31 and 41 and the flow rate controller 74. By way of example, thecontrol unit 150 controls a process of supplying the fluorine-containinggas from the gas supply unit 72 a into the plasma processing space S andetching the wafer W with plasma of the fluorine-containing gas. Further,for example, the control unit 150 controls a process of supplying thehydrogen-containing gas from the gas supply unit 72 b into the palmsprocessing space S and reducing, with plasma of the hydrogen-containinggas, a nickel-containing material deposited on a member (for example,the processing vessel 11, the electrode plate 51, and the focus ring20), of which a surface is arranged to face the plasma processing spaceS, after etching the wafer W. Furthermore, for example, the control unit150 controls a process of supplying the oxygen-containing gas from thegas supply unit 72 c into the plasma processing space S and removing,with plasma of the oxygen-containing gas, nickel, which is obtained byreducing the nickel-containing material.

Further, the program is stored in a computer readable storage mediumsuch as a hard disk (HD), a flexible disk (FD), a compact disk (CD), amagneto-optical disk (MO), a memory card or the like and may beinstalled in the control unit 150 from the computer readable storagemedium.

Hereinafter, a configuration example of the wafer W to be etched in theplasma processing apparatus 1 will be explained. FIG. 2 is a diagramillustrating a configuration example of the wafer to be etched in theplasma processing apparatus in accordance with the example embodiment.As depicted in FIG. 2, the wafer W includes a nickel silicide film D1, asilicon nitride film D2, a silicon oxide film D3, a silicon nitride filmD4, a silicon oxide film D5, a resist film D6, and a gate electrode G1.

The nickel silicide film D1 is a base film constituting source/drainregions for field effect transistor (FET). On a surface of the nickelsilicide film D1, the silicon nitride film D2, the silicon oxide filmD3, the silicon nitride film D4, the silicon oxide film D5, and theresist film D6 are stacked in sequence. Although the present exampleembodiment illustrates an example where the silicon nitride film D2 isformed on the surface of the nickel silicide film D1, a silicon oxidefilm may be formed on the surface of the nickel silicide film D1.

The silicon nitride film D2 and the silicon nitride film D4 are etchstop films. The silicon oxide film D3 and the silicon oxide film D5 areinterlayer insulating films. The resist film D6 is a mask film on whicha preset pattern is formed. In the silicon nitride film D2, the siliconoxide film D3, the silicon nitride film D4, and the silicon oxide filmD5, multiple contact holes C1 for FET are formed corresponding to thepattern of the resist film D6.

The gate electrode G1 includes a gate insulating film G11, a gatepolysilicon film G12, and a sidewall insulating film G13.

Meanwhile, in the above-described plasma processing apparatus 1, inorder to form the contact hole C1 in the wafer W, the wafer W is etchedtoward the nickel silicide film D1 with the resist film D6 as a mask. Inthe plasma processing apparatus 1, if the wafer W is etched toward thenickel silicide film D1 serving as a base film, the contact hole C1reaches the nickel silicide film D1 and the nickel silicide film D1itself may be etched. If the nickel silicide film D1 is etched, anickel-containing material generated from the nickel silicide film D1 isdeposited on members (for example, the processing vessel 11, theelectrode plate 51, and the focus ring 20) of which surfaces arearranged to face the plasma processing space S. If the nickel-containingmaterial is accumulatively deposited on the members of which thesurfaces are arranged to face the plasma processing space S, plasmadensity within the plasma processing space S may be varied. As a result,etching characteristics of the wafer W may be degraded (changed) with alapse of time. Hereinafter, explanation on this matter will be provided.Further, in the following descriptions, as an example of a member ofwhich a surface is arranged to face the plasma processing space S, theelectrode plate 51 of the upper electrode 42 will be explained, but itis not limited thereto. In the present example embodiment, a member ofwhich a surface is arranged to face the plasma processing space S canalso be applied to other members such as the processing vessel 11 andthe focus ring 20.

FIG. 3 is an explanatory diagram illustrating a mechanism of degradation(change) of etching characteristics of the wafer with a lapse of timewhen the nickel-containing material is deposited on the electrode plateof the upper electrode. FIG. 3 illustrates that an O₂ gas is supplied asan etching process gas into the plasma processing space S to be excitedinto plasma in a state where the nickel inclusion is deposited on theelectrode plate 51 of the upper electrode 42. In FIG. 3, a particlemodel 110 is a model of nickel contained the nickel-containing materialdeposited on the electrode plate 51. Further, a particle model 120 is amodel of oxygen contained in the O₂ gas. Furthermore, a particle model122 is a model of an oxygen radical contained in the plasmarized O₂ gas.Moreover, a particle model 124 is a model of an electron contained inthe plasmarized O₂ gas.

As depicted in FIG. 3, in a state where the nickel-containing materialis deposited on the electrode plate 51 of the upper electrode 42, theoxygen radical contained in the plasmarized O₂ gas is inactivated by thenickel contained in the nickel-containing material. That is, the oxygenradical expressed by the particle model 122 is attracted to the nickelexpressed by the particle model 110. The nickel-containing materialreacts with the oxygen radical to be deposited as a nickel oxide such asNi₂O₃ on the electrode plate 51. Therefore, the plasma density withinthe plasma processing space S in the state where the nickel-containingmaterial is deposited is reduced as compared with a state where thenickel-containing material is not deposited. As a result, an amount ofoxygen radicals supplied toward the wafer W is reduced, so that etchingcharacteristics, such as an etching rate, of the wafer W are degraded(changed) with a lapse of time. Further, FIG. 3 illustrates an examplewhere the O₂ gas is supplied as the etching process gas into the plasmaprocessing space S. However, it is assumed that even if anotherprocessing gas is supplied into the plasma processing space S instead ofthe O₂ gas, the etching characteristics of the wafer W are degraded(changed) with a lapse of time in the same manner. Further, if a metaloxide such as Ni₂O₃ is accumulatively deposited on the electrode plate51 of the upper electrode 42 for plasma generation, an electrostaticcapacitance of the parallel plate type plasma processing apparatus ischanged. As a result, if the same high frequency power is applied, theplasma density may be varied depending on an accumulation amount of themetal oxide film, so that the etching characteristics of the wafer W aredegraded (changed) with a lapse of time.

Subsequently, there will be explained a model example in which thenickel-containing material is deposited on the electrode plate 51 of theupper electrode 42. FIG. 4A and FIG. 4B are diagrams each illustrating amodel example in which the nickel-containing material is deposited onthe electrode plate 51 of the upper electrode 42. FIG. 4A and FIG. 4Billustrate examples where the nickel-containing material such as Ni₂O₃is deposited on the electrode plate 51 after the wafer W is etched. InFIG. 4A and FIG. 4B, a molecule model group 510 is a model of nickeldeposited on the electrode plate 51 after the wafer W is etched.

In the plasma process in accordance with the present example embodiment,there is performed a first process of supplying the fluorine-containinggas (e.g., a C₄F₆ gas or a CH₂F₂ gas, and an O₂ gas) into the plasmaprocessing space S and etching the wafer W with plasma of thefluorine-containing gas. By way of example, in the plasma process, inorder to form the contact holes C1 in the wafer W, the wafer W is etchedtoward the nickel silicide film D1 with the plasma of thefluorine-containing gas with the resist film D6 as a mask. Thus, asdepicted in FIG. 4A, Ni (molecule model group 510) as thenickel-containing material generated from the etched nickel silicidefilm D1 of the wafer W is deposited on the surface of the electrodeplate 51. For this reason, the first process may be referred to as“etching process”.

Further, in FIG. 4B, a molecule model group 530 is a model of hydrogen.

The etching process can be expressed by the following chemical reactionformula (1). Herein, H* denotes a hydrogen radical and CF* denotes a CFradical.NiSi+H*+CF*→Ni+SiH₄+CF*  (1)

As shown in FIG. 4B, the Ni is deposited on the electrode plate 51, andoxidized by a radical of the O₂ gas supplied in the etching process tobe deposited as Ni₂O₃. This deposition process can be expressed by thefollowing chemical reaction formula (2). Herein, O* denotes an oxygenradical.Ni+O*→Ni₂O₃  (2)

Next, there will be explained a model example of a plasma process whenNi₂O₃ as the nickel-containing material is deposited on the electrodeplate 51 after the wafer W is etched. FIG. 5A to FIG. 5C are diagramseach illustrating a model example of a plasma process in accordance withthe present example embodiment. FIG. 5A to FIG. 5C illustrate exampleswhere Ni₂O₃ as the nickel-containing material is deposited on theelectrode plate 51 after the wafer W is etched. In FIG. 5A to FIG. 5C, amolecule model group 610 is a model of nickel contained in Ni₂O₃deposited on the electrode plate 51 after the wafer W is etched.Further, in FIG. 5A to FIG. 5C, a molecule model group 620 is a model ofoxygen contained in Ni₂O₃ deposited on the electrode plate 51 after thewafer W is etched.

In the plasma process in accordance with the present example embodiment,there is performed the first process of supplying thefluorine-containing gas (e.g., a C₄F₆ gas or a CH₂F₂ gas, and O₂) intothe plasma processing space S and etching the wafer W with plasma of thefluorine-containing gas. By way of example, in the plasma process, inorder to form the contact holes C1 in the wafer W, the wafer W is etchedtoward the nickel silicide film D1 with the plasma of thefluorine-containing gas with the resist film D6 as a mask. Thus, asdepicted in FIG. 5A, Ni₂O₃ (the molecule model group 610 and themolecule model group 620) as the nickel-containing material generatedfrom the nickel silicide film D1 of the etched wafer W is deposited onthe surface of the electrode plate 51. For this reason, the firstprocess may be referred to as “etching process”.

Further, in FIG. 5B, a molecule model group 630 is a model of nitrogen.Furthermore, in FIG. 5B, a molecule model group 640 is a model ofhydrogen.

In the plasma process in accordance with the present example embodiment,there is performed the second process of supplying thehydrogen-containing gas (e.g., a H₂ gas) and the nitrogen-containing gas(e.g., at least any one of a N₂ gas, a NH₃ gas, and a N₂H₂ gas) into theplasma processing space S to reduce, with plasma of thehydrogen-containing gas and the nitrogen-containing gas, the Ni₂O₃deposited on the electrode plate 51 after the first process. Thus, asdepicted in FIG. 5B, the Ni₂O₃ on the surface of the electrode plate 51is reduced by the plasma of the hydrogen-containing gas and thenitrogen-containing gas, so that a NH₃OH gas is generated and oxygen isseparated from the Ni₂O₃ on the surface of the electrode plate 51. As aresult, on the surface of the electrode plate 51, oxygen is separatedfrom the Ni₂O₃ and nickel remains. For this reason, the second processmay be referred to as “reduction process”. The reduction process can beexpressed by the following chemical reaction formula (3). Herein, a H₂gas is used as an example of the hydrogen-containing gas, but at leastany one of a CH₃F gas, a CH₂F₂ gas, a CHF₃ gas, a NH₃ gas, and a N₂H₂gas may be used.Ni₂O₃+N₂+H₂→Ni+NH₃OH  (3)

Further, in FIG. 5C, a molecule model group 650 is a model of carbon.Furthermore, in FIG. 5C, a molecule model group 660 is a model ofoxygen.

In the plasma process in accordance with the present example embodiment,there is performed the third process of supplying the oxygen-containinggas (e.g., a CO₂ gas) into the plasma processing space S and removingthe nickel, which is obtained by reducing Ni₂O₃ in the second process,with plasma of the oxygen-containing gas. Thus, as depicted in FIG. 5C,the nickel remaining on the surface of the electrode plate 51 chemicallyreacts with the plasma of the oxygen-containing gas, so that a Ni(CO)₄gas as a complex gas is generated and the nickel is removed from thesurface of the electrode plate 51. For this reason, the third processmay be referred to as “removal process”. The removal process can beexpressed by the following chemical reaction formula (4).Ni+CO₂→Ni₂O₃+Ni(CO)₄  (4)

As described above, in the plasma process and the plasma processingapparatus 1 of the present example embodiment, the fluorine-containinggas is supplied into the plasma processing space S and the wafer W isetched with the plasma of the fluorine-containing gas in the firstprocess. Further, in the plasma process and the plasma processingapparatus 1 of the present example embodiment, the hydrogen-containinggas is supplied into the plasma processing space S and thenickel-containing material deposited on the electrode plate 51 after thefirst process is reduced with the plasma of the hydrogen-containing gasto remain the nickel on the surface of the electrode plate 51 in thesecond process. Furthermore, in the plasma process and the plasmaprocessing apparatus 1 of the present example embodiment, theoxygen-containing gas is supplied into the plasma processing space S,and the nickel, which is obtained by reducing the nickel-containingmaterial in the second process, is removed with the plasma of theoxygen-containing gas to generate the Ni(CO)₄ gas as a complex gas inthe third process. For this reason, in accordance with the presentexample embodiment, even if the nickel-containing material generatedfrom the wafer W during the etching process is deposited on variousmembers facing the plasma processing space S, it is possible to removethe nickel-containing material from the members. Therefore, it ispossible to suppress the variation in the plasma density within theplasma processing space. As a result, in accordance with the presentexample embodiment, it is possible to suppress the etchingcharacteristics of the wafer W from being degraded (changed) with alapse of time.

Further, in the plasma process and the plasma processing apparatus 1 ofthe present example embodiment, the hydrogen-containing gas and thenitrogen-containing gas may be supplied into the plasma processing spaceS in the second process, and the nickel-containing material deposited onthe electrode plate 51 after the first process may be reduced with theplasma of the hydrogen-containing gas and the nitrogen-containing gas.For this reason, in accordance with the present example embodiment, evenif the nickel-containing material deposited on various members facingthe plasma processing space S contains Ni₂O₃, it is possible toappropriately reduce the Ni₂O₃ to obtain the nickel.

Hereinafter, an experimental example of the plasma process in accordancewith the present example embodiment will be explained. FIG. 6 is a flowchart of the plasma process in accordance with the experimental example.

In the plasma process in accordance with the experimental example, theetching process is performed (process S101). To be specific, the controlunit 150 controls the flow rate controller 74 a to supply a C₄F₆ gas ora CH₂F₂ gas and an O₂ gas into the plasma processing space S. Then, thecontrol unit 150 controls the first high frequency power supply 30 andthe second high frequency power supply 40 to excite the C₄F₆ gas or theCH₂F₂ gas and the O₂ gas into plasma to etch the wafer W with the plasmaof the C₄F₆ gas or the CH₂F₂ gas and the O₂ gas.

Then, in the plasma process in accordance with the experimental example,the reduction process is performed using a hydrogen-containing gas and anitrogen-containing gas (process S102). To be specific, the control unit150 controls the flow rate controllers 74 b and 74 d to supply a H₂gas/a N₂ gas into the plasma processing space S at a flow rate of 50sccm/300 sccm, respectively. Then, the control unit 150 controls thefirst high frequency power supply 30 and the second high frequency powersupply 40 to excite the H₂ gas/the N₂ gas into plasma to reduce Ni₂O₃deposited on the electrode plate 51 facing the plasma processing space Swith the plasma of the H₂ gas/the N₂ gas.

Thereafter, in the plasma process in accordance with the experimentalexample, the removal process is performed (process S103). To bespecific, the control unit 150 controls the flow rate controller 74 c tosupply a CO₂ gas into the plasma processing space S. Then, the controlunit 150 controls the first high frequency power supply 30 and thesecond high frequency power supply 40 to excite the CO₂ gas into plasmato remove the nickel, which is obtained by reducing the Ni₂O₃, with theplasma of the CO₂ gas.

In the plasma process in accordance with the experimental example, thewafer W is etched through the etching process, and the Ni₂O₃ depositedon the electrode plate 51 is reduced through the reduction process, sothat the nickel remains on the surface of the electrode plate 51. Then,the nickel as a complex gas Ni(CO)₄ can be removed through the removalprocess. For this reason, in the plasma process in accordance with theexperimental example, even if the nickel-containing material generatedfrom the wafer W during the etching process is deposited on theelectrode plate 51, it is possible to remove Ni₂O₃ contained in thenickel-containing material with high efficiency. Therefore, it ispossible to suppress the variation in the plasma density within theplasma processing space S. As a result, it is possible to suppress theetching characteristics of the wafer W from being degraded with a lapseof time. Although the experimental example illustrates an example wherea set of the reduction process using the hydrogen-containing gas and thenitrogen-containing gas and the removal process is performed one timeafter the etching process, the set of the reduction process using thehydrogen-containing gas and the nitrogen-containing gas and the removalprocess may be repeatedly performed two or more times after the etchingprocess.

Then, an effect of the plasma processing method in accordance with thepresent example embodiment will be explained. FIG. 7 is a diagram (firstdiagram) for explaining an effect of the plasma processing method inaccordance with the present example embodiment. FIG. 7 illustrates thevariation in Vpp on the wafer W in the case of performing the plasmaprocess in accordance with the present example embodiment. Herein, theVpp denotes a difference between the maximum value and the minimum valueof a voltage in the high frequency power on the surface of the wafer W.In FIG. 7, a vertical axis represents the Vpp (V) of the wafer W, and ahorizontal axis represents a date on which the Vpp on the wafer W ismeasured. It can be found out that the Vpp (V) correlates with theplasma density caused by the high frequency power, and it can be foundout that the variation in the Vpp (V) corresponds to the variation inthe plasma density.

A graph group 710 of FIG. 7 shows a relationship between the Vpp on thewafer W and a date when a dry cleaning (DC) process is performed to thewafer W by an O₂ gas without performing the plasma process in accordancewith the present example embodiment. A graph group 720 shows arelationship between the Vpp on the wafer W and a date when the plasmaprocess of the present example embodiment is performed after the DCprocess is performed.

As shown in the graph group 710, when the DC process is performedwithout performing the plasma process in accordance with the presentexample embodiment, the Vpp on the wafer W is decreased with a lapse ofthe measuring date. It is assumed that this is because thenickel-containing material generated from the nickel silicide film D1 ofthe wafer W during the etching process is accumulatively deposited onthe various members facing the plasma processing space S, so that theplasma density within the plasma processing space S is varied.

Meanwhile, in the case of performing the plasma process in accordancewith the present example embodiment, the nickel-containing materialdeposited on the electrode plate 51 is removed through the reductionprocess and the removal process. As a result, as shown in the graphgroup 720, the Vpp on the wafer W has the substantially same as the Vppcorresponding to the date “3/1” on which the Vpp on the wafer W ismeasured. It is assumed that this is because even if thenickel-containing material generated from the nickel silicide film D1 onthe wafer W during the etching process is deposited on the variousmembers facing the plasma processing space S, the nickel-containingmaterial is appropriately removed from those members.

FIG. 8 is a diagram (second diagram) for explaining an effect of theplasma processing method in accordance with the present exampleembodiment. A horizontal axis in FIG. 8 represents a lot number of thewafer W loaded into the plasma processing apparatus 1, and a verticalaxis represents the Vpp (V) on the wafer W.

In FIG. 8, a graph 810 shows a relationship between the Vpp on the waferW and the lot number of the wafer W in the case of performing a DCprocess without performing the plasma process in accordance with thepresent example embodiment. A graph 820 shows a relationship between theVpp on the wafer W and the lot number of the wafer W in the case ofperforming the plasma process in accordance with the present exampleembodiment.

Through the comparison between the graph 810 and the graph 820, thedecrement in the Vpp on the wafer W in the case of performing the plasmaprocessing method in accordance with the present example embodiment issmaller than the decrement in the Vpp on the wafer W in the case ofperforming only the DC process. In this example embodiment, thedecrement in the Vpp on the wafer W in the case of performing the plasmaprocessing method in accordance with the present example embodiment isdecreased by 72% as compared with the decrement in the Vpp on the waferW in the case of performing only the DC process. It is assumed that thisis because in the case of performing the plasma process in accordancewith the present example embodiment, even if the nickel-containingmaterial generated from the nickel silicide film D1 on the wafer Wduring the etching process is deposited on the various members facingthe plasma processing space S, the nickel-containing material isappropriately removed from those members.

EXPLANATION OF REFERENCE NUMERALS

1: Plasma processing apparatus

11: Processing vessel

20: Focus ring

30: First high frequency power supply

40: Second high frequency power supply

42: Upper electrode

51: Electrode plate

52: Electrode supporting body

72: Processing gas supply source

72 a, 72 b, 72 c, 72 d: Gas supply units

74 a, 74 b, 74 c, 74 d: Flow rate controllers

150: Control unit

D1: Nickel silicide film

D2, D4: Silicon nitride film

D3, D5: Silicon oxide film

W: Wafer

We claim:
 1. A plasma processing method performed in a plasma processingapparatus, the plasma processing method comprising: a first process ofsupplying a fluorine-containing gas into a plasma processing space togenerate plasma of the fluorine-containing gas and etching a targetsubstrate, in which at least one of a silicon oxide film and a siliconnitride film is formed on a surface of a nickel silicide film, with theplasma of the fluorine-containing gas; a second process of supplying ahydrogen-containing gas into the plasma processing space to generateplasma of the hydrogen-containing gas and reducing, with the plasma ofthe hydrogen-containing gas, a nickel-containing material deposited on amember, of which a surface is arranged to face the plasma processingspace, after the first process; and a third process of supplying anoxygen-containing gas into the plasma processing space to generateplasma of the oxygen-containing gas and removing nickel, which isobtained by reducing the nickel-containing material in the secondprocess, with the plasma of the oxygen-containing gas, wherein variationin Vpp on the target substrate is suppressed by removing thenickel-containing material deposited on the member, of which the surfaceis arranged to face the plasma processing space, through the secondprocess and the third process.
 2. The plasma processing method of claim1, wherein the second process and the third process are repeatedlyperformed at least twice.
 3. The plasma processing method of claim 1,wherein the second process is performed by supplying thehydrogen-containing gas and a nitrogen-containing gas.
 4. The plasmaprocessing method of claim 3, wherein the nitrogen-containing gas is atleast one of a N₂ gas, a NH₃ gas, and a N₂H₂ gas.
 5. The plasmaprocessing method of claim 1, wherein the hydrogen-containing gas is atleast one of a H₂ gas, a CH₃F gas, a CH₂F₂ gas, a CHF₃, a NH₃ gas, aN₂H₂ gas.
 6. The plasma processing method of claim 1, wherein theoxygen-containing gas is at least one of an O₂ gas, a CO₂ gas, and a COgas.
 7. A plasma processing apparatus comprising: a processing vesselconfigured to partition a plasma processing space accommodating thereina target substrate, in which at least one of a silicon oxide film and asilicon nitride film is formed on a surface of a nickel silicide film; afirst gas supply unit configured to supply a fluorine-containing gasinto the plasma processing space; a second gas supply unit configured tosupply a hydrogen-containing gas into the plasma processing space; athird gas supply unit configured to supply an oxygen-containing gas intothe plasma processing space; and a control unit configured to perform afirst process of supplying the fluorine-containing gas into the plasmaprocessing space from the first gas supply unit to generate plasma ofthe fluorine-containing gas and etching the target substrate with theplasma of the fluorine-containing gas; a second process of supplying thehydrogen-containing gas into the plasma processing space from the secondgas supply unit to generate plasma of the hydrogen-containing gas andreducing, with the plasma of the hydrogen-containing gas, anickel-containing material deposited on a member, of which a surface isarranged to face the plasma processing space, after the first process;and a third process of supplying the oxygen-containing gas into theplasma processing space from the third gas supply unit to generateplasma of the oxygen-containing gas and removing nickel, which isobtained by reducing the nickel-containing material in the secondprocess, with the plasma of the oxygen-containing gas, and configured tosuppress variation in Vpp on the target substrate by removing thenickel-containing material deposited on the member, of which the surfaceis arranged to face the plasma processing space, through the secondprocess and the third process, wherein the variation in the Vpp on thetarget substrate is suppressed by removing the nickel-containingmaterial deposited on the member, of which the surface is arranged toface the plasma processing space, through the second process and thethird process.
 8. The plasma processing apparatus of claim 7, whereinthe hydrogen-containing gas is at least one of a H₂ gas, a CH₃F gas, aCH₂F₂ gas, a CHF₃, a NH₃ gas, and a N₂H₂ gas.